The present invention is directed to the fabrication of thick-film and multilayer ceramic devices. It particularly concerns the formation of the dielectric layers of such devices.
The thick-film process is used to provide packages for individual integrated circuits as well as to interconnect a plurality of such circuits. In accordance with the thick-film process, conductive paths for providing the connections among the various terminals of the integrated circuits are deposited on substrate materials, a dielectric layer is applied over the conductive paths, and further conductive paths are then deposited over the dielectric material so as to form a three-dimensional connection structure.
There are a number of reasons why it is desirable from a mechanical and heat-transfer point of view to employ ceramic material, as opposed to organic resins, as the dielectric. However, ceramic materials are less desirable than organic ones in one respect, namely, their relatively high dielectric constant. The high dielectric constant results in a high capacitance between the conductive paths at various levels, and it limits the maximum speed of the circuitry that can be embodied in the thick-film device.
To reduce this drawback but still obtain the advantages of ceramic dielectrics, U.S. Pat. No. 4,781,968 to Kellerman proposed to embed hollow glass microspheres in the ceramic material. The presence of the microspheres reduces the effective dielectric constant of the resultant dielectric layer and thus increases maximum circuit speed. I hereby incorporate that patent by reference.
In the method described in that patent, the microspheres are mixed with a composition comprising ceramic or a glass/ceramic composite matrix material disposed in a conventional thick-film organic carrier vehicle, and the mixture is deposited over conductive paths formed on a substrate. The resultant structure is then fired.